1. Field of the Invention
The present invention relates to a wet type frictional engagement device.
2. Description of the Related Art
As a wet type frictional engagement device, a lockup clutch of a torque converter and a clutch or a brake to engage, disengage or lock a component of an automatic transmission are known.
However, in the above conventional wet type frictional engagement devices, only one of a pair of friction plates which are frictionally engaged with each other in a case filled with oil is pushed against the other friction plate by a predetermined force, and no oil is forcibly fed between the friction plates.
Accordingly, in the engagement or semi-engagement of the conventional frictional engagement device, a sufficient quantity of oil is not fed between the friction surfaces. As a result, a film of oil of an appropriate thickness can not be stably formed on the friction surfaces, and a friction coefficient between the friction surfaces is apt to change. Therefore, especially in a state of semi-engagement, what is called "judder" is caused in the clutch, and it becomes impossible to operated the clutch smoothly.